This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/JP99/02947 which has an International filing date of Jun. 2, 1999, which designated the United States of America.
This invention relates to a paper bulking promoter with which sheets of paper obtained from a pulp feedstock can be bulky without reducing the effect of a sizing agent.
Recently, there is a desire for high-quality paper, e.g., paper excellent in printability and voluminousness. Since the printability and voluminousness of paper are closely related to the bulkiness thereof, various attempts have been made to improve bulkiness. However pulp recycling is made to be impossible as well as smoothness of a paper is made to be impaired. Although a paper bulking promoter containing a certain alcohol and/or a polyoxyalkylene adduct thereof was also disclosed (WO98/03730), it may be associated with an insufficiency in exerting the effect of a sizing agent employed generally in combination. Furthermore, a bulking promoter, which is a fatty acid polyamide polyamine, is an available commercially, but has only a limited performance.
An object of the present invention is to provide a paper bulking promoter by which sufficient bulking effect can be obtained even when the bulking promoter is added in a small amount and which does further not reduce the performance of a sizing agent added in paper-preparing step.
Thus, the invention provides a paper bulking promoter comprising an ester compound having the melting point of not more than 100xc2x0 C. selected from (A) an ester compound of a polyhydric alcohol and a fatty acid and (B) an ester compound of a polyhydric alcohol and a fatty acid further including from more than 0 mole to less than 12 moles on the average of C2-4 alkylene oxide (hereinafter referred as OA) groups per 1 mole of the said ester compound.
According to the paper bulking promoter of the present invention, an excellent bulking effect can be obtained even when the paper bulking promoter is added in a small amount, and a bulky sheet can be obtained without impairing an effect of a sizing agent.
An ester compound of the paper bulking promoter in the present invention is:
(A) an ester compound of a polyhydric alcohol and a fatty acid (an ester compound having no OA group) having the melting point of not more than 100xc2x0 C., or,
(B) an ester compound of a polyhydric alcohol and a fatty acid, further including from more than 0 mole to less than 12 moles on the average of C2-4 OA groups per 1 mole of the said ester compound and having the melting point of not more than 100xc2x0 C.
Both members as (A) and (B) of these esters may be used in combination, and two or more of each member of esters may also be used.
A polyhydric alcohol as a constituent of an ester compound in the present invention is preferably a 2- to 14-hydric alcohol having 2 to 24 carbon atoms in total which may contain an ether group. A 2-hydric (dihydric) alcohol may be one which has 2 to 10 carbon atoms in total and which may contain an ether group, such as propylene glycol, dipropylene glycol, butylene glycol, dibutylene glycol, ethylene glycol, diethylene glycol and polyethylene glycol. Then, 3-(tri) or more hydric alcohol may be one which has 3 to 24 carbon atoms in total, which may contain an ether group and wherein the total number of hydroxy group/the total number of carbon atoms=0.4 to 1 in one molecule, such as glycerol, poly(n=2 to 5)glycerol, pentaerythritol, dipentaerythritol, arabitol, sorbitol, stachyose, erythrite, arabite, mannite, glucose and sucrose. Preferably, there are ethylene glycol, diethylene glycol, propylene glycol, and an alcohol which has 3 to 12 carbon atoms in total, which may contain an ether group, wherein the total number of hydroxy group/the total number of carbon atoms=0.5 to 1 in one molecule, and which is 3- or more hydric alcohol. More preferably, there are glycerol, poly (n=2 to 4) glycerol and pentaerythritol.
Further, a fatty acid constituting an ester compound of the present invention may be a fatty acid having 1 to 24 carbon atoms, preferably 10 to 22 carbon atoms. It may be any one of saturated, unsaturated, linear and branched one. A linear saturated fatty acid is particularly preferable. More preferably, there are lauric acid, stearic acid, palmitic acid, myristic acid and behenic acid.
The ester compound of the present invention may be obtained by carrying out of conventionally known esterification and adding of alkylene oxide. For example, a mixture of a fatty acid and a polyhydric alcohol is, if necessary, admixed with an esterification catalyst and reacted at 150 to 250xc2x0 C. to obtain an ester compound (A), to which an alkylene oxide is added in the presence of an alkaline catalyst, whereby obtaining an alkylene oxide adduct (B). Alternatively, an esterification reaction may be carried out, after an alkylene oxide is added to a fatty acid or a polyhydric alcohol. Furthermore, it can be sometimes obtained by only adding an alkylene oxide to a fatty acid, too.
The average esterification degree of an ester compound in the present invention is more than 0. Preferably, per 1 mole of a polyhydric alcohol, OH in the alcohol has been esterified in an amount of 10 to 95% by equivalent. An alcohol has particularly preferably 1 to 2 moles of a fatty acid group per 1 mole of polyhydric alcohol.
When an ester compound (B) containing an OA group having 2 to 4 carbon atoms is used as a paper bulking promoter of the present invention, the number thereof (OA group) is on the average from more than 0 to less than 12 moles, preferably not more than 6 moles, and actually preferably 0.1 to 6 moles, per 1 mole of the ester compound. When a polyhydric alcohol, which can become an OA group, such as ethylene glycol, is used, the mole numbers thereof are also counted as the number of OA groups. An OA group is formed by adding an alkylene oxide having 2 to 4 carbon atoms. A preferred alkylene oxide is ethylene oxide (EO) or propylene oxide (PO). These may be used as any one of EO, PO and a mixture of EO and PO. In the present invention, it is particularly preferable to use an ester compound containing no OA group as a paper bulking promoter.
An ester compound of the present invention has HLB of preferably 1 to 14, more preferably 1.5 to 10, further preferably 2 to 8. HLB is an index for the hydrophilicity of a surfactant. The larger the value of HLB is, the higher the hydrophilicity becomes. In the present invention, the HLB of each compound is calculated by the following formula according to Griffin""s method.   HLB  ⁢      xe2x80x83    =                    Molecular        ⁢                  xe2x80x83                ⁢        weight        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        hydrophilic        ⁢                  xe2x80x83                ⁢        group        ⁢                  xe2x80x83                ⁢        moiety                    Molecular        ⁢                  xe2x80x83                ⁢        weight        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        ester        ⁢                  xe2x80x83                ⁢        compound              xc3x97    20  
And, in the present invention, a hydrophilic group means the following group in an ester compound.
(1) xe2x80x94(CH2CH2O)mxe2x80x94
(2) xe2x80x94(RO)nxe2x80x94 [R: alkylene group having 3 to 4 carbon atoms,
n less than 2.0, wherein n is a total number in one molecule]
For example, the underlined part in RCOOxe2x80x94(PO)1-5H represents a hydrophilic group. On the other hand, the underlined part in RCOOxe2x80x94(PO)2-0H represents a hydrophobic group.
Further, in the case of the following formula: 
any PO group is a hydrophobic group since one molecule contains 2 moles of PO in total.
(3) A group derived from an alcohol which may have an ether group, which is a 3- or more hydric alcohol having 3 to 24 carbon atoms in total, and wherein the total number of hydroxy group/the total number of carbon atoms=0.4 to 1 in one molecule.
(4) An oxygen atom adjacent to a carbonyl group.
An ester compound of the present invention has the melting point of 100xc2x0 C. or lower, preferably xe2x88x9215xc2x0 C. or higher and 80xc2x0 C. or lower, more preferably 20xc2x0 C. or higher and 70xc2x0 C. or lower, from the viewpoint of handleability and preserving a sizing performance. The melting point is made to be a temperature of peak beginning, when a solid ester compound pre-cooled is measured (temperature raising ratio of 2xc2x0 C./minute) by a differential scanning calorimeter (DSC).
An ester compound of the present invention is preferably one having HLB of 2 to 8 and the melting point of 10 to 70xc2x0 C., and more preferably one having HLB of 2 to 7 and the melting point of 45 to 70xc2x0 C. Within such range, more preferable results of the bulk promoting effect and the sizing effect (maintained effect of a sizing agent) can be obtained.
A paper bulking promoter of the present invention is added at any step of papermaking. When it is a liquid product, it may be added as it is. Then, when it is a solid product, it may be added after pulverizing, fusing by heat or diluting with water etc. Further, if necessary, a nonionic, anionic, cationic and polymeric surfactant, and preferably a nonionic surfactant, may be used as an emulsifier or dispersant. In such case, the ratio of a paper bulking promoter in the present invention and a surfactant is: [a paper bulking promoter of the present invention]/surfactant=99.5/0.5 to 70/30 (by weight), preferably 98/2 to 80/20.
The bulking promoter of the present invention is applicable to a variety of ordinary pulp feedstocks ranging from virgin pulps such as mechanical pulps including TMP (thermomechanical pulp) and chemical pulps including LBKP (bleached hardwood pulp) to pulps prepared from various waste papers. The point where the bulking promoter of the present invention is added is not particularly limited as long as it is within the papermaking step. The papermaking step is to form paper layers by draining water from a diluted liquid of a pulp feedstock throughout the advance thereof on a wire netting. In a factory, for example, the bulking promoter is desirably added at a point where it can be evenly blended with a pulp feedstock, such as, refiner, machine chest, or headbox. After the bulking promoter of this invention is added to a pulp feedstock, the resultant mixture is subjected as it is to sheet forming. The bulking promoter remains in the paper. The paper bulking promoter of this invention is added in an amount of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the pulp feedstock. But, in the case of some system, an excellent bulking effect can be obtained by adding a small amount of 0.1 to 1% by weight.
The pulp sheet obtained by using the paper bulking promoter of the present invention has a bulk density (the measurement method is shown in the Examples given later) lower by preferably at least 5%, more preferably at least 7%, than the product not containing the paper bulking promoter.
At the time of papermaking, it is allowable to add a sizing agent such as a rosin, an alkyl ketene dimer, gelatin, starch and latex, moreover a filler, a yield improver, a drainability improver, a paper strength improver, and the like. A sizing agent fills voids on the surface or bulk of the paper with a water-proof material to suppress the permeation of water or inks, and can be used for paper-treatment by adding to a pulp slurry (inner sizing) or coating onto a resultant paper (surface sizing). A sizing agent is added usually in an amount of 0.01 to 1.0% by weight based on a pulp feedstock, although the amount may vary depending on the types of the paper. Since a paper bulking promoter of the present invention is excellent also in preserving a sizing performance, it is applied preferably to a method for producing an obtainable highly bulky pulp sheet using a sizing agent in combination.